(1) Field of the Invention
This invention relates to a process for the purification of food processing wastewater and the recovery of proteinaceous materials, fats and oils therefrom. More particularly, this invention relates to the use of a combination of a soluble lignin or a halogen and natural or synthetic polymers to coagulate and flocculate proteinaceous materials, fats and oils from the wastewaters of food processing plants.
(2) Description of the Prior Art
Processing water from poultry plants, cattle slaughter houses, rendering plants, seafood processing plants, other food processing plants, such as margarine and soya bean processing plants, and the like all discharge wastewater which pollutes the waterways without proper treatment but the effluent contains proteinaceous materials, fats and oils which, if recovered, can be used in economically valuable animal feed. For example, the material recovered from poultry wastewater may contain from 30 to 35% true proteins and from 24 to 45% fat. The amino acid composition of the poultry wastewater by-product is similar to soybean meal. "Ultrafiltration Treatment of Poultry Processing Wastewater and Recovery of a Nutritional By-Product," J. C. Shih et al. Poultry Science, Volume 59, pages 247-252 (1980).
Efforts to reduce the environmental problems associated with food processing wastewater by removing proteinaceous materials, fats and oil has been ongoing for many years. For example, such efforts are reported by Messrs. H. O. Halvorson, A. R. Cade, and W. J. Fullen, "Recovery of Proteins From Packinghouse Waste by Super-Chlorination", Sewage Works Journal, Vol. 3, pages 488-501 (1931), in which coagulation of proteins using chlorine and other halogens is described.
Various forms of lignin have also been used as coagulating and flocculating agents to treat wastewater. For example, U.S. Pat. No. 2,200,784 teaches flocculation of aqueous liquids carrying colloidal material, such as sewage, with solubilized alkaline lignin and adjusting the mixture pH to 6.5 or less. In U.S. Pat. No. 2,471,474 water-soluble alkali lignin is combined with proteins to form a precipitate and used to purify and clarify beverages. U.S. Pat. No. 3,850,799 teaches the use of lignins cross-linked with polyoxyalkylene linkages as flocculating agents in wastewater treatment.
Other types of compounds have also been used in the recovery of proteinaceous materials, fats and oils from wastewater. For example, U.S. Pat. No. 4,061,568 teaches the use of acid hydrolyzing metal salts, such as iron (Fe.sup.+3) and aluminum (Al.sup.+3) salts as flocculating agents for recovery proteins from fat refining plants, margarine and other food processing plants. The metal salt forms a complex with the proteins and fats in wastewater which has been acidified; the complex is precipitated with calcium hydroxide; and the complex is separated as a sludge by sedimentation, centrifugation or flotation.
U.S. Pat. No. 4,933,087 describes a process for coagulating and flocculating proteins and fats in food processing wastewater by acidifying the wastewater, adding an alginate, allowing the wastewater to react, adding activated biological sludge to improve the coagulating properties of the floc, e.g. floc size. Additional materials including hydrated lime, finely-milled peat, acidified peat or activated carbon may also be used in the process.
It is the general object of this invention to provide a process for removing proteinaceous materials, fats and oils from food processing wastewater by admixing acidified wastewater with a coagulating compound and a natural or synthetic polymer.
Another object of this invention is to provide a process for producing a material suitable for use in animal feed.
A further object of this invention is to provide a process of treating a wastewater stream from a food processing plant whereby the BOD, ammonia, oil and grease content, and suspended solids (in the effluent water) are substantially reduced.
Other objects, features and advantages of the invention will be apparent from the following details of the invention as more fully described.